Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | December 29

by Marc Rayman


Pardawn Me, Dear Readers,

Far away from Earthlings who look forward to a new year, Dawn looks forward to a new world. On the far side of the sun, the interplanetary explorer is closing in on Ceres, using its advanced ion propulsion system to match solar orbits with the dwarf planet.

Since breaking out of orbit around the giant protoplanet Vesta in September 2012, the spaceship has patiently flown in interplanetary cruise. That long mission phase is over, and now Dawn is starting the Ceres chapter of its extraordinary extraterrestrial expedition. Configured for its approach phase, the craft is following a new and carefully designed course described in detail last month. In March it will slip ever so gracefully into orbit for an ambitious and exciting exploration of the alien world ahead.

Over the past year, we have provided previews of the major activities during all the phases of Dawn’s mission at Ceres. This month, let’s take a look at Ceres itself, an intriguing and mysterious orb that has beckoned for more than two centuries. Now, finally, after so long, Earth is answering the cosmic invitation, and an ambassador from our planet is about to take up permanent residence there. Over the course of Dawn’s grand adventure, our knowledge will rocket far, far beyond all that has been learned before.

There can be two accounts of Ceres: its own history, which dates back to near the dawn of the solar system almost 4.6 billion years ago, and its history in the scope of human knowledge, which is somewhat shorter. Both are rich topics, with much more than we can cover here (or in the first log for this entire mission), but let’s touch on a few tidbits. We begin with the latter history.

In 1800, the known solar system contained seven planets: Mercury, Venus, Earth (home to some of our readers), Mars, Jupiter, Saturn and Uranus. This reflected a new and sophisticated scientific understanding, because Uranus had first been noticed in telescopes not long before, in 1781. (The other planets had been known to ancient sky watchers.) Even before William Herschel’s fortuitous sighting of a planet beyond Saturn, astronomers had wondered about the gap between Mars and Jupiter and speculated about the possibility of a planet there. Although some astronomers had searched, their efforts had not yielded a new planet.

Giuseppe Piazzi

Giuseppe Piazzi points the way to his discovery, the planet Ceres. (Dawn’s route there is more complex than Piazzi might have guessed.) Credit: Osservatorio Astronomico di Palermo

Astronomer Giuseppe Piazzi was not looking for a planet on Jan. 1, 1801, but he spotted an unfamiliar dot of light that wandered slowly among the stars. He named it for Ceres, the Roman goddess of agriculture, and if you had cereal this morning, you have already had an etymological connection with the goddess.

The Dawn project worked with the International Astronomical Union (IAU) to formalize a plan for names on Ceres that builds upon and broadens Piazzi’s theme. Craters will be named for gods and goddesses of agriculture and vegetation from world mythology. Other features will be named for agricultural festivals.

Because Ceres was fainter than the other known planets, it was evident that it was smaller. Nevertheless, many astronomers considered it to be a planet too.

It is worth noting the significance of this. Modern astronomy had chanced upon only one other planet, so Piazzi’s discovery was A Big Deal. When a new chemical element was found a couple of years later, it was named cerium in tribute to the new planet Ceres. (Uranus had been similarly honored with the 1789 naming of uranium. That element’s peculiar property of emitting radiation would not be known for another century.)

In the six years following the discovery of Ceres, three more bodies were detected orbiting between Mars and Jupiter. (One of them is Vesta, now known in spectacular detail thanks to Dawn’s extensive exploration in 2011-2012.) There then ensued a gap of more than 38 years before another was found, so for well over a generation, the sun’s family of planets was unchanged.

So if you had been reading about all this 200 years ago, there would have been at least two important differences from now. One is that your Internet connection would have been considerably slower. The other is that you might have learned in school or elsewhere that Ceres was a planet.

In 1846, a planet was discovered beyond Uranus, and we call it Neptune. Nothing else of comparable size has subsequently been seen in our solar system.

With scientific knowledge and technology progressing in the middle of the nineteenth century, new objects were glimpsed between Mars and Jupiter. As more and more were seen over the years, what we now know as the main asteroid belt was gradually recognized. Terminology changed too. One of the great strengths of science is that it advances, and sometimes we have to modify our vocabulary to reflect the improved, refined view of the universe.

By the time Pluto was sighted in 1930, Ceres had long been known as a “minor planet” and an “asteroid.” For a while thereafter, Pluto enjoyed planetary status similar to what Ceres had had. In fact, in 1940, scientists named two more additions to the periodic table of the elements neptunium and plutonium. While the histories are not identical, there is a certain parallel, with more and more objects in Pluto’s part of the solar system later being found. Terminology changed again: Pluto was subsumed into the new category of “dwarf planets” defined by the IAU in 2006. Ceres was the first body to be discovered that met the criteria established by the IAU, and Pluto was the second. (Spacecraft are now on their way to both dwarf planets: Dawn to orbit Ceres 214 years after its discovery and the wonderful New Horizons mission to fly past Pluto 85 years after it was found.)

Four views of Ceres taken by the Hubble telescope

Four views of Ceres as it rotates, as seen with Hubble Space Telescope, are the best we have so far. (The brightest feature has been exaggerated here.) As summarized in October, Dawn’s pictures will surpass this quality within a month, revealing details never seen before. Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), and L. McFadden (University of Maryland, College Park)

We discussed this new nomenclature in some detail shortly after it was adopted. We understand that the designation then, as now, is controversial among some scientists and the public, and there are strong emotions on this topic. We will not delve into it here (nor in the blog comments below), preferring instead to focus on the extraordinary successes of science, the great power of the scientific method and the thrill of bold adventures far from home. The Dawn team remains both unperturbed and confident in what to call this intriguing and alluring world: we call it “Ceres.” And our goal is to develop that faint smudge of light amidst the stars into a richly detailed portrait.

One of the advances of science was the recognition that Ceres really is entirely different from typical residents of the main asteroid belt. It is a colossus! There are millions upon millions of asteroids, and yet Ceres itself contains roughly 30 percent of the mass in that entire vast region of space. By the way, Vesta, the second most massive body there, constitutes about eight percent of the asteroid belt’s mass. It is remarkable that Dawn will single-handedly explore around 40 percent of the asteroid belt’s mass.

With an equatorial diameter of about 605 miles (975 kilometers), a value that Dawn will refine very soon, Ceres is the largest body between the sun and Pluto that a spacecraft has not yet visited. It is occasionally described as being comparable in size to Texas, which is like comparing a basketball to a flat sheet of paper. Ceres has a surface area 38 percent of that of the continental United States, or four times the area of Texas. (Nevertheless, until Dawn shows evidence to the contrary, we will assume Texas has more rodeos.) It is nearly a third of the area of Europe and larger than the combined lands of France, Germany, Italy, Norway, Spain, Sweden and the United Kingdom. Such an expansive place offers the promise of tremendous diversity and many marvelous and exciting sights to behold. Earth is about to be introduced to a fascinating new world.

How did Ceres come to be? And why is that being phrased as a question instead of a more declarative introduction to the history and nature of this dwarf planet? For that matter, why is this paragraph composed exclusively of questions? At least this sentence isn’t a question, right? OK, really, shouldn’t we stay more on topic?

At the dawn of the solar system almost 4.6 billion years ago, the young sun was surrounded by a swirling cloud of dust and gas. Sometimes some particles would happen to hit and stick together. Then more and more and more particles would stick to them, and eventually these agglomerations would grow so large that their gravity would pull in even more material. It was through mechanisms like this that the planets formed.

But when massive Jupiter developed, its powerful gravity terminated the growth of objects nearby, leaving bits and pieces as asteroids. Ceres and Vesta, already sizable by then, might have grown to become even larger, each incorporating still more of the nearby material, had Jupiter not deprived them of such an opportunity. Not having made it to full planetary proportions, Ceres and Vesta are known as protoplanets, and studying them provides scientists with insight into the largest building blocks of planets and into worlds that are intriguing in their own rights.

Artist's concept of formation of asteroids

Dust and gas surrounding the sun coalesced into planets and asteroids, as depicted in this artist’s view. Credit: William Hartmann, Courtesy of UCLA

Ceres apparently formed far enough from the sun under conditions cool enough for it to hang on to water molecules. Indeed, scientists have good reason to believe that water (mostly in the form of ice) may make up an astonishing 30 percent of its mass. Ceres may contain more water than Mars or any other body in the inner solar system except Earth. (Comets, of course, have high proportions of water too, but they are so minuscule compared to this behemoth that each one harbors a quite negligible amount of water when measured against Ceres’ huge inventory.)

Although some of the moons of the outer planets also are ice and rock, and they display very interesting characteristics to the impressive and capable spacecraft that have flown past (in some cases repeatedly, as the craft orbited the host planet), no probe has had the capability to linger in orbit around any of them. Dawn’s in-depth exploration of Ceres will yield more detailed and complete views than we have obtained of any icy moon.

Radioactive elements incorporated into Ceres when it was forming would supply it with some heat, and its great bulk would provide thermal insulation, so it would take a very long time for the heat to escape into space. The sun, faraway though it is, adds still more heat. As a result, there may be some water warm enough to be liquid. (The concentration of any chemical impurities in the water that affect its freezing point, as salt does, may make an important difference in how much is liquid.) This distant, alien world may have lakes or even oceans of liquid water deep underground. What a fantastic possibility!

There will be no liquid on the frigid surface. Even ice on the surface, exposed to the cold vacuum of space, would sublimate before long. But ice could be just beneath the surface, perhaps well less than a yard (a meter) deep.

Ceres then may have a thin, dusty crust over a mantle rich in ice that might be more than 60 miles (100 kilometers) thick. Its warmer core is likely composed mostly of rock.

As heat dissipated from Ceres’ interior over the eons, it may have undergone convection, with the warmer material rising and cooler material sinking very slowly. This is reminiscent of what occurs in pot of heated water and in Earth’s interior. Even if it did occur at some time in Ceres’ history, it probably is not happening any longer, as too much heat would have been lost by now, so there would not be enough left to power the upward movement of warm material. But the convective process might have written its signature in structures or minerals left behind when ice sublimated after being pushed to the surface. Dawn’s photos of geological features and measurements of the composition may provide a window to forces in the interior of the protoplanet sometime in its past.

Even if convection is no longer occurring, Ceres is not entirely static. We have very tantalizing information from a marvelously productive far-infrared space telescope named for the only known astronomer who found a planet before Piazzi made his discovery. The Herschel Space Observatory recently detected a tiny amount of water vapor emanating from the distant dwarf planet. Scientists do not know how the water vapor makes it into space. It might be from ice sublimating (possibly following a powerful impact that exposed subsurface ice) or perhaps from geysers or even erupting cryovolcanoes (“cold volcanoes”) powered by heat that Ceres has retained since its formation. In any case, Herschel saw water, albeit in very, very small quantity.

It is not certain whether water vapor is there all the time. It is unknown whether, for example, it depends on solar heating and hence where Ceres is in its somewhat elliptical orbit around the sun (not as circular as Earth’s orbit but more circular than Mars’), which requires 4.6 years to complete.

Even if the water vapor is present during Dawn’s 1.3-year primary mission in orbit, it would be extremely difficult to detect. Herschel made its findings when our ship was already far, far from Earth, well along its interplanetary itinerary. The probe’s sensors were designed for studying the solid surfaces of airless bodies, not an exceedingly tenuous veil of water molecules. For context, the water vapor Herschel measured is significantly less dense than Earth’s atmosphere is even far above the International Space Station, which orbits in what most people consider to be the vacuum of space. Dawn will not need windshield wipers! Nevertheless, as we saw in February, the Dawn team, ever creative and dedicated to squeezing as much out of the mission as possible, investigated techniques this year that might be effective in searching for an exceptionally thin vapor. They have augmented the plan with many hours of observations of the space above Ceres when the spacecraft is over the night side during its first science orbit in April and May at an altitude of 8,400 miles (13,500 kilometers). It is possible that if there is some water vapor, the instruments may pick up a faint signature in the sunlight that passes through it.

Regardless of the possibility of detecting traces of water from Ceres, Dawn will focus its measurements on the uncharted surface and the interior, as it did at Vesta. Vesta displayed landscapes battered by craters from impacts during more than 4.5 billion years in the rough and tumble asteroid belt. Ceres has spent most or all of its history also in the asteroid belt, but it is possible it will not show its age so clearly. Ice, although very hard at such low temperatures, is not as hard as rock. So it may be that the surface gradually “relaxes” after an impact, just as your skin restores its shape after pressure has been removed. Craters older than a few tens of millions of years may have slowly disappeared. (That may sound old, but it is a small fraction of Ceres’ lifetime.) Near the poles, where it is colder so ice is harder, the scars of impact craters may be preserved for longer.

Ceres has more than water-ice and rock. It probably contains organic materials, some produced by chemical processes with the minerals already there and some delivered by asteroids that fell to its surface. This is noteworthy, because water and organic chemicals are ingredients for life. The combination of Ceres’ internal heat and the weak but persistent heating from the sun provides energy, which also is essential for life. Even if the possibility of life itself there is extremely remote (and it is beyond Dawn’s capability to detect), the conditions for “prebiotic” chemistry would be tremendously interesting. That is why, as we explained in August, we want to protect the special environment on the ground from contamination by the terrestrial chemicals in our orbiting spacecraft.

Image of Ceres taken by the Dawn spacecraft.

Dawn acquired this picture of Ceres on Dec. 1, as described last month. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

While there is more known about Ceres, there is much, much more that is unknown. Dawn seeks to discover many of the secrets of this unfamiliar, fascinating member of the solar system family. One of the measures of its success would be if, upon answering many of our questions about Ceres, we are left with even more questions. Now on the threshold of an old world which will be new to us, we do not have long to wait for the great rewards of new knowledge, new insight, new thrills and new mysteries to solve.

Dawn is 382,000 miles (614,000 kilometers) from Ceres, or 1.6 times the average distance between Earth and the moon. It is also 3.77 AU (351 million miles, or 564 million kilometers) from Earth, or 1,500 times as far as the moon and 3.84 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and three minutes to make the round trip.

Dr. Marc D. Rayman
8:00 a.m. PST December 29, 2014

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79 Responses to “Dawn Journal | December 29”

  1. Alan quayle says:

    Hi marc
    Just interested to hear if you will be able to characterise Ceres internal composition with enough accuracy, to tell if there is still an existing subsurface ocean. Wild speculation at the moment, I know, but would be an awesome discovery, given europas radiation environment and the great distance of enceladus, Ceres may be catapulted to number one target for follow up missions.

    • Marc Rayman says:

      Hi Alan,

      I agree that it would awesome to discover evidence of an ocean!

      If Dawn does find such evidence, it will not be on the basis of direct characterization of the deep interior composition but rather though other means. What Dawn measures directly about the interior of Ceres is the distribution of mass, so we can sense regions of different density. (This is how we do it.) Water, of course, has a different density from rock or ice. Still, I am very doubtful that this method would be accurate enough to find an ocean of credible size on Ceres. Our other instruments measure composition up to about a yard (a meter) beneath the surface, which is much to shallow to find liquid water. But science is very powerful, so there are other possibilities. For example, there might be signs in the chemical composition or shape of geological features at the surface that water has risen up through cracks.

      The scientific community will do its best to turn the wealth of data Dawn will gather into real knowledge about Ceres. Is there an ocean there now? Was there one in the past? What else will we find? I don’t know, but whatever the answers are, I’m confident there will be many awesome discoveries.


      • Dave Lyons says:


        I saw where another poster said a new photo session would occur in six days. Is that true, and if so, is that six days from January 19? I am eager to see more pictures, no matter their resolution. Now that Dawn is drawing close, is there a reason why photo sessions are not more frequent?



        • Marc Rayman says:

          Hi Dave,

          Yes, our next photo session will be on Jan. 25. You might find my comment below to be helpful. In my next Dawn Journal, I will give still more details on the plan for the remaining photo sessions.

          We have a very compelling reason for not taking more pictures. Dawn has lost two of its four reaction wheels. I have written about this extensively (see here for more information and links), but in brief, the extraordinary flight team has devised plans to accomplish all of the original Ceres objectives despite this unforeseen challenge. One part of the solution is to conserve hydrazine by rotating the spacecraft only when truly necessary. Taking pictures requires turning from the orientation needed for ion thrusting to the orientation needed for pointing the camera at Ceres, then to the orientation needed for pointing the main antenna to Earth so we can transmit the pictures, and then back to the orientation needed for ion thrusting. We will acquire many, many thousands of pictures from our observational orbits, as I described in February, May, June and August, so the overall portrait we will develop of Ceres will not be compromised by taking fewer during the approach phase.


          • Dave Lyons says:


            Thanks for taking the time for the detailed explanation. Excited to see Ceres when Dawn is in orbit.

      • The same week: disappearance of Leonard Nimoy “Spock” and the discovery the lights of Ceres by the probe Dawn
        I propose to call the lights of Ceres “Spock Lights”
        Vote for this .

  2. Sean Deany says:

    A very embryonic movie footage of Ceres. The white spot shown is clearly Region A a possible cryovolcanic area, but still very puzzling as its certainly a central peak in a deep impact basin. Perhaps due to localised cryovolcanism the central peak receives a good share of water ice fallout thus reflected by sunlight? Also Piazzi’s white spot may possibly be some similar phenomena. Backing up my own speculations and still only such when regarding Ceres oblate spheroid shape there appears to be more material violently ejected from its southern hemisphere – like Vesta. Of course its rapid rotation and being a icy body has driving factors as well. The Keck spectra image of 10 years ago somewhat pointed to this vaguely although I have never read any references to such. My theory and I’m no geologist is that while the southern hemisphere of 1 Ceres may have more material blasted off and have lower altitudes from datum level the northern hemisphere is probably far smoother, while indeed may posses numerous craters, it may show evidence of containment of water ice close to the surface. From the Hubble images it appears that the northern polar region has frost. Thankfully all this speculation and theorising may come to a head soon.

  3. Matt says:

    Thank you Dr.Rayman,

    great! I am happy about this movie! Mr. Danielle seems to be right. My impression is that in the lower part of Ceres’ globe we can see two or three significant impact crater (nearby the darker strutures, but not identical to it, one of it up t 100-200 km diameter). I am really surprized how significant this “white” feature appears again. The next photo “session” in about six days shall bring some clarification.



  4. Fantastic Movie image, Dawn staff! I am happy!
    I compared the image of today (383’000Km), with the first images of Vesta at 483’000 and 264’000 Km. Considering that Vesta also seemed slightly smooth, but then turned out to be heavily cratered, I expect the same for Ceres.
    Ceres appears more ‘Oblated of how I imagined..
    That feature very bright in North region, is the same that you notice in Hubble – Telescope.
    I don’t think it is Piazzi crater, but the the area nominated “Region A”.
    Good Work!

    • Marc Rayman says:

      Thank you, Daniele.

      It is difficult not to draw conclusions from these distant images, but I will not take the time here to offer my own speculations about what we will see. Our experience in exploring the cosmos is often that our early impressions change when we get better views. I expect Vesta and Ceres to be quite different from each other (which, of course, is the reason to explore both of them), but we will know more soon!

      The shape of Ceres in these pictures may not be what you expected because it is only partially illuminated from Dawn’s perspective, just as the moon is not always full from our vantage point on Earth. In my next Dawn Journal, I will describe the viewing geometry for all of Dawn’s approach photos.


  5. Guillaume Vollant-Boulé says:

    Hello Marc, I want to thank you or the incredible effort you put down to write those journals. I would have never known about Dawn if wasn’t for your talk on NASATV in 2014 and even if the budget for public relation is almost inexistent, your doing a wonderful job to make this mission as visible as possible and that’s awesome!!!

    I have also a question. It seems that a lot of science mission like Dawn or Hubble seem to have gyros problem, are people at NASA trying to find why this happens and how to make better ones, or is this problem inherent to gyroscope in general and cannot be fixed?

    Thank you again,
    Guillaume Vollant-Boulé

    • Marc Rayman says:

      Thank you for your very kind message, Guillaume. I’m glad you like my Dawn Journals. They (and the comments here) take a fair amount of my free time, but it’s worth it to share the profundity and excitement of this mission with others. I’m also glad you saw my presentation. (Other Dawnophiles may enjoy it too. It is archived here.)

      There have been problems with reaction wheels (a form of gyroscope) on a number of missions, some sponsored by NASA and some from other organizations. As I commented last month, those problematic devices are not being used on new spacecraft, and engineers have new designs that are reliable. Fortunately, as you can see if you follow the links back, thanks to the tremendous work of the Dawn flight team, we now have very solid plans that will allow us to complete all of our original objectives at Ceres, regardless of the health of our reaction wheels. I’ll have a little more good news about this in my next Dawn Journal too.

      Thank you again, and I’m pleased to have you along on this amazing interplanetary voyage.


      • Guillaume Vollant-Boulé says:

        Thank you for responding. The Dawn team as been the most responsive to questions and feedbacks in all of the current interplanetary missions, keep it up!!! I find it amazing how you can do thing in a way nobody imagine could be possible.

        CANNOT wait for the first close-up pictures of Ceres!!!

        With best regards from Qc, Canada.

  6. Matt Gibbons says:

    Hi Marc,

    A quick one (I promise!). When do you expect to begin resolving surface features? I would assume you have a good model based on Vesta, for when 1000 meter features begin to come into focus and so on. As of this writing, Dawn is officially under 200,000 miles from Ceres, so I would guess that in a week or two some coarse resolution will be revealing features better than Hubble.

    One last one…based on what I’ve read, Ceres has an axial tilt of approximately 3°, while Vesta has a tilt of 29° (is that correct?). I recall that Dawn took advantage of it’s time in orbit of Vesta to see areas near the poles that were initially hidden in shadow due to it’s tilt. It looks like that problem is almost non-existent with Ceres, yes?

    Thanks so much and waiting “patiently” for the coming images!!!


    • Marc Rayman says:

      Hi Matt,

      My next Dawn Journal will have more on the resolution of the images during the approach phase. In the meantime, at the risk of stating the obvious, “resolving surface features” depends on their sizes. Vesta and Ceres are entirely different, and the appearance of the surface on the world we have already explored tells us virtually nothing about what to expect at the one ahead. The optical design of Dawn’s camera, of course, is extremely well understood. To pick up your example, one camera pixel is 1,000 meters or about 0.6 miles (in the official units of the website but not the Dawn project) at a distance of around 6,600 miles (a little under 11,000 kilometers). That’s one pixel, which wouldn’t show much. The answer changes in proportion to distance (and feature size), so if you want that same feature to be two pixels, then you need to be half the distance. To make the feature 10 pixels wide, Dawn would need to take its picture at one-tenth the distance. (As a reminder, Dawn ultimately will fly down to a circular orbit at an altitude of 230 miles, or 375 kilometers.) The resolution of the images we acquire later this month will be better than what Hubble could see. Again, there will be more on this in my next Dawn Journal.

      You’re quite right about the issues of axial tilt (which cause seasons, as the sun moves north and south of the equator). Ceres’ axis is tilted much less than Vesta’s. Dawn determined Vesta’s tilt to be 27 degrees. We will measure Ceres’ very soon, but, yes, it does appear to be around 3 degrees. (For comparison, Earth’s is 23 degrees.) As you know, by orbiting Vesta for so long rather than conducting a brief flyby, we could wait to see terrain that became illuminated as the protoplanet’s seasons progressed and the sun slowly advanced to the north. (With its longer year than ours, Vesta’s seasons last an average of 11 months each.) I wrote more about this in May and June 2012 (and it even was part of a simulated problem for the flight team in preparing for Vesta.) Because Ceres’ axial tilt is so small, the portion of the surface near the pole that’s hidden in the darkness of winter night will be tiny indeed.


      • Matt Gibbons says:

        Marc, your journal is really valuable to us on the sidelines of this incredible mission. Your time is greatly appreciated…now, if you don’t mind, I’ll ask for a bit more ;)

        Thinking about the axial tilts of Vesta and Ceres being so different it makes me think of the images of Vesta and how literally hammered it has been over time. Rheasilvia and Veneneia craters being the most significant. Would polar hits like this help to explain the abundant tilt angle of Vesta. It seems to me if a body takes a hit perpendicular to the equator, the amount of tilt increase would be minimal compared to the same hits at the poles. This is kind of stream of conscience, since I really don’t know what I’m talking about…just a layman’s drift I guess. Succinctly, would Vesta’s violent history explain the amount of tilt. Since no meteors have ever been identified as being from Ceres, and many identified as being from Vesta…well, it seems to make sense to me that Ceres, for whatever reason doesn’t seem to have been in the same shooting gallery that Vesta has/was.



        • Marc Rayman says:

          Thank you, Matt. As you kindly recognize the time it takes to respond to so many comments (I do have a full time job too), I will keep this reply brief.

          The axial tilts of planets vary widely and are the result of many forces over the planets’ histories. Powerful collisions are one part of the complicated story but other contributors are internal geophysical processes and the gravitational effects of moons (if any), other planets and the sun. I already gave the tilts for Earth, Vesta and Ceres below, but consider also that Mercury’s is zero degrees, Venus’ is 177 degrees and Mars’ is 25 deg. There’s no one reason. Scientists recognize that the tilts of some planets change dramatically too. So to understand Vesta’s and Ceres’ tilts, a large number of factors would need to be considered.


  7. indique says:

    Hey Team, thanks for sharing such a wealth of information. Does Dawn rely only on its panels for computational and transmit power, or is there another source? I find it quite amazing you are able to detect and decode such transmissions over such distance, and recently through the solar furnace. What sort of data rates are happening? How close is it to predictions? Does Dawn do much on-board image processing? If you only counted the research value of the observing and transmitting/receiving over that distance, it is already a remarkable contribution. And add all the subject observation on top of that – wow!
    Soon Ceres will add one to its number of moons. I wonder how Ceres will react to the new arrival.

    cheers, Indique

    • Marc Rayman says:

      I share your admiration, Indique, for what human ingenuity has achieved. It is remarkable that we can operate spacecraft so amazingly far away. (For others, Indique’s reference to the solar furnace is that Dawn recently was on the opposite side of the sun from Earth.)

      Dawn’s sole source of electrical power is from its solar arrays, as I explained at the beginning of this blog and in this overview of the power system.

      The telecommunications system is a marvel. At its maximum rate, using a 5-foot (1.5-meter) antenna and a 100-watt radio, Dawn transmits about 124 kilobits per second to Earth, comparable to Internet speeds used by inhabitants of the previous century. (And as I described in October, when using an auxiliary antenna, the rate is one thousand times slower than a modem from 20 years ago.) The rate at which we can transmit instructions and other data to the spacecraft varies but is always much less. The maximum is two kilobits per second. The spacecraft’s capability to communicate with the Deep Space Network is slightly better than we predicted when we were building it. Complex and impressive as it is, this is well understood technology.

      There is no real image processing onboard. The images (as well as the other science data) are compressed, thereby reducing somewhat the number of bits that need to be transmitted without sacrificing quality, but that is the extent of it.

      You are quite right that Ceres is about to receive a new moon! I’ve had the same thought. You might enjoy my description of Dawn’s arrival at Vesta, including (at the end) a commentary on the search for a moon.

      Thank you for your interest and for participating in this amazing journey!


      • indique says:

        Thanks very much for your response and pointers to all the details. The stuff that dreams are made of. I’ve come very recently to follow your project following some exposure in APOD, and now even more impetus to go back and read all past posts.

        All the best with this adventure!

        fyi, you made it into today.

  8. Bianchino Daniele says:

    I have calculated, imagining, that if Ceres was a satellite of the Earth, to see this as big as the moon in the sky, it should be at about 108,000 km from Earth..
    that’s Right marc Rayman?
    and would probably be a stable satellite.
    but this is fantasizing …
    Be patient, friends, the images won’t ever take too many days to arrive .. :-)

    • Marc Rayman says:

      You are right, Daniele. Ceres’ average diameter is around 27 percent of the moon’s, so if Ceres were about 27 percent of the moon’s distance from Earth, it would look as big as the moon.

      Soon Dawn will be much closer to Ceres even that that!


  9. Mark Raphael says:

    Hi Marc:

    Just checking Dawn’s webiste, to see if any new pictures have been posted yet. The pictures that I and other readers have been whining about for months now!

    I check now, even more so, (not just because of the new pictures). Given recent news events, it is so much nicer to read about us humans getting along to accomlish great things.

    How long do you think it will take for Dawn’s scietific discoveries to be collected, analyzed and then printed in scientific journals? Pictures are wonderful but so is what’s behind the pictures.


    • Marc Rayman says:

      I wasn’t aware of any whining, Mark; I’ve mostly heard enthusiasm and eagerness, which I share! I indicated to Ben (just below this comment) that the standard process is going on now, and we will post a picture on this website and elsewhere as soon as it’s ready.

      It generally takes around a year from receiving the data to complete the first analyses, write the papers, and then have them published in journals. Papers are presented at conferences sooner than that.

      As an illustration, Dawn arrived in orbit at Vesta in July 2011, and the first scientific papers from our exploration there were published the following May. But we collected such a wealth of data that the majority of Vesta papers are still in the future. Indeed, five new Vesta papers were submitted to a journal just this week. More will be submitted next week. Papers using Dawn’s data from Vesta and Ceres likely will be published for many, many years to come.

      Thank you for your interest!


  10. Ben says:

    OK, I know we are only halfway through the month, but… …what’s the update? Did Dawn successfully stop thrust and acquire a new picture of Ceres? Has that picture been recieved at this point? How long does it take to download a picture froom Dawn? Can you guess when this new picture will be made available? The ‘Where is Dawn’ page graphic appears to show that thrusting will stay off for a little while – why was that and is that still the plan? Thanks and Regards, Ben

    • Marc Rayman says:

      Hi Ben,

      Dawn is continuing its approach to Ceres smoothly. The spacecraft is healthy and accomplishing all planned activities, including capturing images and spectra. The team has to receive and process the images before making them public, following established processes.

      The reason for the graphic showing the thrust off is a little complicated and ultimately not that interesting (in my opinion). It’s mostly a quirk of the software and its relation to how we plan different segments of the trajectory during the approach phase. I can assure you that ion thrusting is continuing. Dawn’s most common activity in this mission phase is ion thrusting to follow the complex route to its first observational orbit (and it will be shown correctly in the graphic most of the time). When it is not thrusting, it will either be conducting one of its imaging sessions or communicating with Earth. I’m sorry for the confusion, but I appreciate that you use Where is Dawn Now? to stay up to date!


    • Robert Griner says:

      I’m with Ben. I’m dying to see our next glimpse of the way out spherical goddess of grain!!

  11. Philio Astra says:

    With Dawn in the approach phase to Ceres and New Horizons now awake for Pluto, 2015 is starting out as an exciting year and will only get better. Unlike Dawn, New Horizons will be a flyby. I saw a question and answer about slowing down New Horizons posted somewhere. The basics amounted to: fuel required to get the needed delta v becomes a mass issue and it spirals from there. This leaves me thinking, could a mission be practically designed to enter Pluto orbit (or do a slow flyby) using ion propulsion powered by a large RTG? What sort of time scale would be required for it?

    • Marc Rayman says:

      I share your excitement. The first two dwarf planets discovered are now on the verge of being unveiled. This is the year of the dwarf planet!

      You’re right that Dawn will be able to spend a very long time at Ceres, orbiting it and studying it in detail. New Horizons will gather as much data as it can during its flight past Pluto, and I have every confidence it will be fantastic too! I explained a bit about the challenges of using ion propulsion farther from the sun here. I think that should answer most of your question. The time scale for that or any mission depends on detailed design decisions for things like the particular rocket used, how much electrical power is available for thrusting, how massive the spacecraft is, and myriad other choices that need to be made. All this analysis must occur in the context of the mission objectives and involves trade-offs in cost and risk. Right now, since we don’t have systems that can affordably provide the needed power for any practical ion propulsion in that part of the solar system, I can’t give you a simple answer for what the time scale would be.

      But fortunately the missions that are real and in flight now are going to return spectacular pictures and other data very soon!

  12. Mark Gaponoff says:

    Today I noticed that Dawn is closer to Ceres than the Moon to Earth. A naked-eye observer straddling Dawn would see a disk 1/3 the size of the Moon as seen from Earth, and some surface details would show. Looking forward to pictures from Dawn.

    • Marc Rayman says:

      Mark, you are quite correct. Dawn is now about the same distance from Ceres as the average separation between Earth and the moon. Soon, we’ll see what new sights Dawn is treated to!

      As a reminder to everyone (not specific to your comment), Dawn does not carry a high-power telescope with a narrow field of view. The camera has a relatively low magnification but covers a broad area. The probe is designed to map alien worlds from close orbit.

      • Romana Starfield says:

        Thanks for this post Marc. You anticipated our obvious next questions which would have been along the lines of “If we can see details of the Moon from Earth, why can’t Dawn see more details of Ceres?” Clearly the camera wasn’t designed for that usage. Thanks for letting us know. I am anticipating new photos as much as I am anticipating a nice week off soon in Fiji. Both can not come soon enough!
        Thanks for keeping us informed.

  13. Toma Bandin says:

    Today is that BIG day! 13th January. Day when Dawn should snap that 27 pixel image of Ceres. And we are at 383.000 km, much closer than Earth’s Moon apogee.
    Can you please tell me at what distance will Dawn be from Ceres on Jan 25th when next approach image is to be taken?

    Thank you!

    • Marc Rayman says:

      You’re right, Toma, Dawn stops ion thrusting today to take its first optical navigation images of Ceres. Like you, I can’t wait to see them! Later, the spacecraft will transmit those (and other) valuable bits to distant Earth where they eventually will be turned into pictures that we’ll all get to see when they are ready for release. They will be posted on this website (and elsewhere).

      In my January Dawn Journal I will give the details (including distance) for all the imaging sessions planned for the approach phase. For today’s pictures, as you correctly observed, Dawn is 238,000 miles (383,000 kilometers). (That’s actually just slightly less than the average distance between Earth and the moon.) The next ones will be taken at a range of about 147,000 miles (237,000 kilometers).

      I’d say today is one of the BIG days. Dawn has had many, and many more are ahead!

  14. Sean Deany says:

    Over 230 minor planets in our solar system are known to have moons and there are approx 84 in the asteroid belt – with 5 minor planets having two moons. Therefore it may not come as a surprise that 1 Ceres also has at least one natural satellite and certainly quasi satellites like the Earth. Perhaps Proserpina may become the known moon of 1 Ceres. If there were to be say two moons of 1 Ceres, very small as not to have yet been detected, perhaps they should be named by the International Astronomical Union as Liber and Libera. It was the late Republican era Roman – Cicero who described Liber (male) the guardian of plebeian freedom and Libera (female) goddess of wine, fertility and also freedom, as Ceres’ children. In 2015 the term freedom has great significance worldwide in these troubled times – Liber and Libera may make their selves known to us. I guess it come down to albedo more than size for the reasons as so far there haven’t been moons discovered around Ceres.

    • Marc Rayman says:

      Certainly many bodies in the solar system have been found to have moons, Sean. But there are many other bodies around which moons have not been seen (including Mercury, Venus and Vesta). Telescopic searches from Earth (and Earth orbit) have not detected a moon of Ceres. As I’ve written before, Dawn will conduct its own search from its truly unique vantage point, just as we did at Vesta. We didn’t find any at Vesta, and we might not at Ceres. I don’t think it would be surprising if Ceres had some or none! Only nature knows for sure.

      Your referring to Proserpina must be because of this comment last month. The IAU has not yet established a policy on the naming convention for moons of Ceres, but I am sure many names will be considered if a moon is found.


  15. Nigel Burke says:

    Hello Marc and the Team, I was just reading your comment [below] about sayings we have in English. One local one we use here in Wales, very rarely, is “Never in all my born days…” and never in all My born days did I see such things as you are achieving with this mission. From the Ion Drive that brings a whole new way of interplanetary travel, right through to the end mission of studying, mapping and photographing Ceres.
    As I take in the information you offer I am constantly shaking my head in wonder as science hits brain cells.
    Well done to each and every person involved. A truly inspirational mission. Huge thanks and warmest regards.

  16. Matt Gibbons says:

    Hello Dr. Rayman,

    Seems I read, some time ago, that a third asteroid might have been reached after Ceres. Namely, Pallas. I understand it is in a highly inclined orbit (35 degrees to the ecliptic)…but I’m sure I read that with the proper timing and ion drive resources, a flyby might be possible. No chance for orbit due to the inclination of Pallas…it would take too much fuel to do that. I have also read that it is no longer on the table due to what I’m not quite sure. Timing? Fuel?

    That said, may I assume that Dawn will remain in orbit of Ceres after Dawn takes it’s final bow? Or will it be sent into an independent solar orbit to avoid impacting on Ceres and possibly contaminating it with biological material?

    What are the possibilities presuming that Dawn will complete it’s primary mission and, if left in orbit of Ceres, will have an extended mission?

    Thanks for all the brilliant work. Looking forward to more surprises when Dawn orbits Ceres!

    Matt Gibbons
    Bellingham, WA

    • Marc Rayman says:

      Thank you for your message and your interest, Matt.

      I too have occasionally seen this claim that Dawn might visit Pallas (even for a flyby). This same idea was mentioned here. Pallas was never part of our plan. Indeed, we have never even taken a serious look at it. I don’t know quite how the story originated. It may have been a desire by some people, but no meaningful mission analysis ever supported it. There are good technical reasons such a study would not even have been very worthwhile. Besides, orbiting two uncharted worlds, something never before attempted, is ambitious enough, and we have always recognized that Ceres is so large that the first priority for an extended mission would be to investigate it further.

      You may be confident that Ceres will be Dawn’s permanent home. I wrote about the long-term prospects for the interplanetary traveler here. It is indeed important to ensure it does not impact Ceres, as you mentioned, but we do that by choosing a final orbit that will remain stable.

      We have much to look forward to before then. Plenty of exciting surprises surely are just ahead!


  17. Matt says:

    Only three days until next pictures of Ceres will arrive! Dear Dr. Rayman, I am somewhat proud about my nation’s (Germany) contribution to “Dawn”. I dreamed this night how wonderful it would be, if another important – the Solar system exploring mission – namely “New Horizion” would have your ion drive at board in order to cancel out its high Solar system escaping speed, aiming at an orbit around Pluto. I hope that we will see in future much more usage of the ion drive for missions into outer Solar system, for example to reach fast orbit around Neptun and Uranus and to reach objects in the Kuiper belt.

    Thank you for your contribution to the rise of the ion drive.

    • Marc Rayman says:

      You’re right, Matt. Dawn will acquire some more pictures soon (actually about four days after your comment) using the camera designed and built by our colleagues in Germany. You have good reason to be proud. After the spacecraft transmits the data to Earth and they are processed in Germany into pictures, we will prepare them for release.

      The great benefit of ion propulsion comes about from its conversion of electrical power into thrust. That translates into some significant challenges for operation in the outer solar system, where sunlight is much weaker so electricity is more difficult to generate. I explained this in a little more depth here.


  18. James Kirk says:

    Wow, I’ve just learned about Ceres today from a friend of mine. I was stunned to learn that there is a small planetoid sitting somewhere between Mars and Jupiter that is bigger than Iowa, and Texas combined. Why have we not sent a probe to it before now? I mean I’ve read it is small and all, but really, why the wait? Given that we sent probes out to Jupiter and Mars in the 70s, it seems an awful long time to wait. I am glad you have patience Dr Rayman.
    I await further developments. My friend on the other hand keeps saying “Are we there yet?” They’ve enthused the entire office about this little planet. We have a count down on the office break out area as to when Dawn reaches Ceres. That sort of enthusiasm is geeky, but contagious. Of course with my name he suggested I should boldly go and have a look myself.

    • Marc Rayman says:

      Thank you for your message, James. I share your geeky enthusiasm!

      There are several reasons Ceres has not been visited earlier, even though it has been of scientific interest for such a long time. I’ll offer here an abbreviated explanation.

      While it stands out as the largest unexplored body now in the inner solar system, the earlier solar system missions focused on still larger destinations: the major planets.

      In addition, Ceres is a surprisingly difficult target to orbit. (And it is a long way to go only to fly past it for a brief look, which is how all large bodies have been studied on the first visit. This expedition is the first ever in which humankind has sent a spacecraft to orbit such a massive body without first conducting a reconnaissance with a flyby spacecraft, another of the challenges our team has had to overcome.) The great majority of deep-space missions have gone to Venus and Mars, both of which are significantly easier to get to than Ceres. Not only is Ceres farther away, but the tilt of its orbital plane around the sun relative to Earth’s makes it especially difficult. (I explained this in a little bit more detail here.) Moreover, although it is large compared to most solar system objects, its gravity is weaker than that of the major planets and so it doesn’t help as much in pulling into orbit a spacecraft that’s traveling around the sun.

      For these reasons, a mission to orbit Ceres awaited technological advancements beyond conventional chemical propulsion. Deep Space 1, with its successful testing of ion propulsion on an operational interplanetary mission for the first time, provided the crucial progress. It accomplished a tremendous amount in its own right and paved the way for subsequent ion propelled missions like Dawn. DS1 completed operations in 2001 (shortly after acquiring NASA’s first close-up images of the nucleus of a comet), and a year later NASA provided funding to begin developing Dawn. And now we are almost at Ceres. Our patience is being rewarded.

      Without ion propulsion, a mission only to Ceres (or, for that matter, only to Vesta, which is somewhat more accessible, although still quite a challenge) would be unaffordable within NASA’s Discovery Program of solar system missions. And yet with ion propulsion, we can afford to orbit both, which would otherwise be impossible. No other spacecraft has ever been targeted to orbit two extraterrestrial destinations.

      With regard to the suggestion that you boldly go and have a look, now that you’re onboard Dawn, you are doing exactly that. Welcome! Together we are exploring some of the last uncharted worlds in the inner solar system even though we have known about them for more than two centuries. (I should also mention that I have entitled some of my public presentations on Dawn “To Boldly Go — Well, You Know: NASA’s Dawn Mission to the Asteroid Belt.” And, finally, you might get a kick out of this discussion, which was less accurate and a lot goofier than ours, with a different James Kirk.)


  19. Mark says:

    Marc, thanks for your great blog posts keeping us all up to date on Dawn’s progress and discovery. Saw you on a recent youtube presentation and I gotta say you could easily be the next Carl Sagan making science understandable for the next generation.

    I understand that Dawn has no instruments to detect life but I’m hoping with its camera it’ll easily spot the structures and patterns of a thriving city on (or just under) the surface with an active Cerean culture who will welcome us and share their secret of long life and prosperity. Perhaps they’ll somehow retrieve Dawn, repair its reaction wheels and pump it full of fresh Xenon and Hydrazine and send it back our way attached to a basket full of deliciously out-of-this-world Cerean cookies.

    Resubmitted due to captcha error…

    • Marc Rayman says:

      I greatly appreciate your message, Mark.

      I’ve been in a number of videos, but I assume this recent one is what you saw. I’m very glad you liked it. I certainly do enjoy sharing the thrill of exploration and the excitement of discovery with others, whether in public presentations, as in that video, or in writing.

      I like your fanciful notion for what may occur, but perhaps you should consider that Cereans may have their own version of “planetary protection” protocols (as we do) or other noninterference directives. In any case, I’m disappointingly confident there will be plenty of people who will perceive evidence of life and an active culture even where such evidence is entirely lacking.

      Thank you again.


  20. Marc Elliott says:

    If the Dawn article was written on 12/29/14, and it’s said was 400,000 miles from Ceres at the time, and is traveling at 450 miles per hour; Wouldn’t that place it going into orbit on the 37th day after 12/29/14?

    • Marc Rayman says:

      Thank you for your question, Marc. For others, this is the article he refers to.

      Before I answer, let me try to infer your reasoning. Dawn uses the gentle but continuous thrust of its ion engine to change the spacecraft’s speed every day. Today, the relative speed is just under 400 mph, and it continues to decline. I wrote more about how we use the exquisitely gentle thrust to slip into orbit here.

      I wrote in 2013 the surprising story that it would take Dawn more than five days to accelerate from zero to 60 mph. If you round that to exactly five days, it would mean it changes its velocity by 12 mph per day, so in 37 days, it could accelerate (or, equivalently, decelerate) by 450 mph. Therefore, I presume you concluded that that is how long it would take to get to zero mph and hence into orbit. That actually is a very good line of reasoning! (If that wasn’t your reasoning, then the rest of what I have here may not answer your question, but maybe it’s interesting anyway.)

      The situation is a bit more complicated, which may not be surprising in the execution of an ambitious deep-space expedition. I don’t have room here to give all the details, but let me offer a few tidbits.

      Dawn’s thrust depends on its distance from the sun, which determines how much electrical power its giant solar arrays can produce and hence how much power it can devote to ion thrusting. Now that it is farther from the sun, it can change its speed by about seven mph per day. (So now it would take more than eight days to achieve that same acceleration of zero to 60 mph.) So if the sole objective were to cancel out that 450 mph, it would require about 63 days at today’s power level. The deceleration itself will continue to decrease, as Dawn is still receding from the sun.

      Dawn does not spend all of its time thrusting. Sometimes it pauses thrusting to take pictures and spectra of Ceres. The distant probe also needs to point its main antenna to Earth to radio back its findings and receive a new set of instructions. (During the interplanetary cruise phase, that happened only once every four weeks, but we do it more frequently during the approach phase.) The combination of imaging plus a communications session usually takes between half a day and a day. Therefore, our calculation above of how long it would take to slow down by 450 mph is a little optimistic, because Dawn doesn’t devote every day to ion thrusting.

      As a final detail, the complex choreography to enter orbit does not require the spaceship to go all the way to zero mph relative to Ceres. Ceres’ gravity can take hold even when its dance partner is in motion.

      I hope this overview answers your question.

  21. Toma Bandin says:

    Thank you Marc Rayman and everybody in mission control, thank you for everything! This waiting for Ceres images is almost over.

    I would like to ask you if there is any CHANCE of visiting another asteroid when Ceres exploration is done? I do know it’s a little early but are there any technical chance to do such a thing considering state of spacecraft and quantity of fuel remaining.

    Can’t wait to see that image you are planing to take on Jan 13 and Jan25.

    I wish you all the best!!! Good luck!!!

    • Marc Rayman says:

      Thank you very much, Toma. On behalf of the team, I appreciate your support and good wishes.

      Dawn will not depart Ceres. It will remain in orbit around that distant dwarf planet, eventually becoming what I like to think of as an inert monument to human creativity and ingenuity and our noble spirit of exploration. In August I explained the reasons for remaining there as well as some thoughts about the probe’s fate.

      Before then, we will share in the excitement of the alien world it is about to unveil, and I’m glad you’re engaged in this exciting journey.

  22. Mewo says:

    Excellent read. I have a question: during Dawn’s mission at Ceres, is it likely that another asteroid will approach Ceres closely enough for Dawn to get a look at it?

    • Marc Rayman says:

      Thank you, Mewo.

      Although the asteroid belt is often depicted as being so dense you would need Han Solo’s piloting skills to avoid all the rocks, it isn’t really that way. Space is big! You might find my illustration of how close Dawn would come to any known asteroids on its way to Vesta to be interesting.

      No other objects will come close enough to Ceres to provide Dawn with a good view during its residence there. (Check back here later in the week, and I will give you some specifics.)

      • Mewo says:

        Thanks for the reply. I realize space is big and that even the asteroid belt is pretty much empty. The chances of a chance encounter seemed pretty slim to me, since Dawn didn’t get one on its trip to Vesta or its stay there, but a “freebie” would have been nice. I assume you’ve checked all the other asteroid orbits and already confirmed none of them will make a close approach.

        • Marc Rayman says:

          I promised I would provide an update, Mewo, and here it is. (I hope you have returned to see this.) A colleague of mine and I undertook a special analysis to address your question, analyzing the orbits of 643,953 objects to see what comes closest to Ceres.

          Dawn’s primary mission concludes in June 2016, but we ran our study to the end of 2016 on the chance operations continue for a while (as I mentioned near the end of my August log). During the entire two years, the closest encounter will be with an object known by the evocative name 2001 DK108. On Dec. 28, 2015, its orbit will bring it to a little more than 250,000 miles (400,000 kilometers) from Ceres (and Dawn), which is comparable to the distance between Earth and the moon. 2001 DK108 is estimated to be about one mile (perhaps a bit under two kilometers) in diameter. At that distance, the chunk of rock would be less than one twentieth of a camera pixel across.

          Of the 50 objects that come closest to Ceres, the largest has an estimated diameter of around 6 miles (10 kilometers). (As a matter of personal interest, that’s about the same size as asteroid Rayman.) Impressively known as 1999 VR62, it will be about seven Earth-moon distances from Ceres (1.7 million miles, or 2.7 million kilometers) on Apr. 24, 2015, right about the time Dawn begins its intensive observations in its RC3 orbit. Dawn will be at an altitude of 8,400 miles (13,500 kilometers), and Ceres will nearly fill the camera’s field of view. 1999 VR62 would be about one twenty-fifth of a pixel across.

          So, no surprises here in how far apart objects in the main asteroid belt are, but I thought you might find the quantification of these “close approaches” to be interesting. Fortunately, Dawn will get up very, very close to Ceres, as it did to Vesta, and that will provide us with a wealth of exciting information.

  23. Myles O'Howe says:

    I’m curious about the quality images that will come. Must be exciting to work on a mission sending a robotic spacecraft to a distant body in the solar system. Uncovering mysteries in our solar system must be fun, and take a lot of patient work and planning.

    I wonder if Ceres has some atmosphere.

    • Marc Rayman says:

      The quality will be fabulous, Myles! We took 31,000 pictures at Vesta, and you can browse through many neat ones here. (In fact, with a little more work, you can see nearly all of them here. Scroll down and click on “Launch Vesta Image Browser.”) I described some of what the pictures showed us about Vesta shortly after we departed that giant protoplanet.

      As I have mentioned, our photos in the lowest altitude orbit at Ceres will be more than 800 times better than the best we have from Hubble Space Telescope. We are going to see extraordinary detail on a world that has for more than two centuries been little more than a small, fuzzy blob of light. (If you have the patience to watch a video, you can see an illustration of that improvement in my public lecture on Dawn here.)

      It is indeed very exciting. I know I’m very lucky to work on a mission like this, and my motivation in writing these blogs is to share that excitement and the wonder, the rewards, the challenges, and more with everyone. This mission is for anyone who, like you, longs to know the cosmos.

      The closest thing to an atmosphere detected around Ceres is that extremely thin veil of water vapor I wrote about above. As I indicated, it is much less dense than Earth’s atmosphere even above the International Space Station. So for all practical purposes, Ceres does not have atmosphere.

      Thank you for your interest, and I hope you continue to share in the excitement as we return great pictures and gain many fascinating insights into this distant, uncharted world.

  24. Matt says:

    Hello Dr. Rayman,

    I thank you for the great article. May I propose a wish? It is possible to present a more update picture of Ceres made by Dawn today here at this page? Meanwhile, Dawn has shorten the distance to only 536.000 km. Compared to last month’s pic, Ceres shall appear doubled in size?

    Thanks in advance!


    • Marc Rayman says:

      Thank you for your interest, Matt. Actually, the picture above is the most up-to-date we have. As I explained in detail in December 2013 (with an update in November), Dawn spends most of its time in the approach phase thrusting with its ion propulsion system to enter into orbit around Ceres and then to maneuver to the first major observational orbit. To conserve precious hydrazine, given the loss of two reaction wheels, we stop thrusting only occasionally to take pictures. I summarized the schedule most recently in October.

      We will photograph Ceres twice this month, on Jan. 13 and 25. On that second occasion, the pictures should show slightly more detail than the best we have from Hubble Space Telescope, and of course they will continue to improve after that. Throughout the approach phase, we will post Dawn’s views of Ceres on this website, and I will always include the latest in my Dawn Journals.

      After our very long wait, now Ceres will come into sharper focus very soon!


      • Matt says:

        Thanks, understood, also if it is hard to wait.

        • Marc Rayman says:

          I share your eagerness, Matt. At the same time, I have written in many of my Dawn Journals about the need for patience in this mission, for that is the key to being able to accomplish this truly unique expedition. Ceres has waited for a visitor from Earth for 4.6 billion years. We have managed to wait more than 214 years since discovering the dwarf planet. NASA approved the proposal for the Dawn mission 14 years ago, and after designing, building, and testing this complex spacecraft and planning the ambitious mission, it was launched more than seven years ago. In less than a month, we will have the best pictures ever. By the end of this year, when Dawn is in its lowest orbit, the pictures will be more than 800 times better than the Hubble pictures. Your hard wait will be worth it. Hang on!

  25. byMars says:

    I hope to find life on Ceres!!!

    • Marc Rayman says:

      Perhaps someone will discover evidence of life there sometime on a subsequent mission in the distant future. Dawn carries powerful sensors that will reveal a great deal, but, as I wrote above, the spacecraft does not have the capability to detect life. Fortunately, we do have the capability to discover many other fascinating things about this mysterious world!

  26. jim fletcher says:

    Dear Dr Rayman
    Top stuff by any scientific or literary measure!!
    Very best

  27. Hi Marc, I will be “tuning in” often over the next few months to keep my high school science students up-to-date on Dawn’s mission to Ceres. Thanks for keeping us in the loop. Happy New Year! John Weisenfeld, Science Teacher, Pasco High School, Pasco, WA

    • Marc Rayman says:

      Thank you for bringing your students along on the mission, John! I hope you’ll keep them up to date even beyond the next few months. As I have described in previous Dawn Journals, the spacecraft will be very busy during its complex exploration of this dwarf planet at least through the end of the next school year (June 2016) if all goes well, and there should be a great deal for all of us to see and to learn.

      Happy new year,

  28. That was an excellent read! I’m looking forward to hear more good news during approach phase. Would you mind if I reuse your Dawn Journal in our e-magazine “The Sky Tonight”? – Best wishes and a happy new year
    — Heinz

    • Marc Rayman says:

      I’m glad you found it so interesting, Heinz. Thank you. You are very welcome to reuse this (or anything else on the Dawn website) as long as it’s credited.

      Like you, I’m looking forward to good news during approach. (I hope we’ll have good news during the rest of the Ceres mission as well.) Whatever the news turns out to be, I hope you’ll continue to follow this ambitious adventure.

      With best wishes for your new year,

  29. Ed says:

    Marc, you have excellent technical skills as well as a great ability to communicate. This months column is a wonderful example. Thanks so much for keeping us informed.

  30. Fredda says:

    I’m so excited about the next three months. I’m holding my thumbs to preserve the remaining two reaction wheels (hope it helps as it makes it a bit hard to work and eat :). Happy New Year Dawn! (And let’s by better wheels next time, shall we? :)

    (and thanks for all the posts, Marc!)

  31. eSpace says:

    Your posts are always very informative and also quite a bit of fun. Thank you for keeping us involved and up-to-date! Wishing you and the Dawn Team a very happy, productive, and exciting New Year!

    • Marc Rayman says:

      I appreciate your very kind message. I am delighted to keep you informed, because I want you to be involved. As I’ve written many times, missions like this are for everyone, not only the team doing the work. I’m glad you’re part of the adventure.

      Best wishes to you as well for the new year.

  32. fackförbund says:

    Excellent entry! It’s always nice when you can not only be informed, but also entertained!

  33. Kent Peterson says:

    Hello! I love the Dawn mission. But, I was curious to know when we can expect to see more pictures of Ceres? I can’t wait!

    • Marc Rayman says:

      I very much appreciate your enthusiasm, Kent. And I apologize for this late reply. A website glitch prevented me from receiving your comment sooner. But look at it this way: your wait for my reply consumed part of the time waiting for pictures. Now, their arrival is even sooner!

      In October I gave a summary of the schedule for acquiring images, with the next ones being on Jan. 13. Dawn stores the image data and later transmits its findings to Earth, after which we turn the data into pictures and complete various steps for disseminating them. That all takes a while, but we intend to release photos promptly.